1. Field of the Invention
The present invention relates to a communication system comprised of a plurality of communication apparatuses, the communication apparatus, and a data transmission method.
2. Description of the Related Art
In recent years, streamed data comprised of video signals and audio signals are transmitted using radio communication techniques at home theaters and so on. Because of this, in communication systems each comprised of communication terminals each associated with plural speakers and a control station that controls the terminals, a technique is required by which high-quality video images and musical sounds can be reproduced without interruption and jitter such as communication delay.
In order to satisfy such a requirement, a proposal has been heretofore made that a communication system can be used in which to increase its communication reliability all communication devices within a wireless network transmit identical data through redundant communication paths.
Moreover, a method has been proposed in which to achieve a high communication rate through an increase in radio signal intensity a transmission side transmits to many reception sides by using a wide-band directional antenna and the reception sides direct directional beams to the transmission side by using narrow-band directional antennas.
On the other hand, in order to maintain good communication quality at all times through redundant transmission, polarization-, code-, or frequency-multiplex transmission is used. For example, a technique is devised by which good communication quality is maintained even when there is physical shielding in the communication path. In such a technique, communication shielding is avoided by redundantly transmitting identical data at plural senders through polarization-multiplex transmission and using polarization diversity reception at receiving terminals (see, for examples, Japanese Patent Laid-Open No. 11-274994).
Furthermore, as another example, there is a method in which at a redundant structure including a radio line where communications are carried out with a reserve line when an active line has been disconnected, different polarizations of the same frequency band are assigned thereto. In the above case, by using the transmission line comprised of the active line and the reserve line to which the different polarizations of the same frequency band are assigned, a state is brought about in which when one of both lines has been disconnected, the other line takes the place thereof and, thus, the efficiency of frequency resource usage is enhanced (see, for example, Japanese Patent Laid-Open No. 2001-86051).
However, in a communication system in which a control station and a plurality of communication devices perform broadcast communications, when the control station and the communication devices have antenna directivity, sufficient link quality cannot be obtained depending on the arrangement of the devices and, thus, communication between them has not been established at times.
Therefore there is a need to increase the number of communications with the other communication devices within the system to increase redundancy and further increase communication reliability until all the communication devices within the communication system can surely receive identical data at a sufficient link quality. However, since there is a trade-off relationship between the reliability of communication lines and the number of communications, such a method is inefficient. And further, as the number of communications increases in order to increase the reliability, communication time lengthens.